Electrostatic chuck having reduced power loss

ABSTRACT

Embodiments of the invention generally relate to an electrostatic chuck having reduced power loss, and methods and apparatus for reducing power loss in an electrostatic chuck, as well as methods for testing and manufacture thereof. In one embodiment, an electrostatic chuck is provided. The electrostatic chuck includes a conductive base, and a ceramic body disposed on the conductive base, the ceramic body comprising an electrode and one or more heating elements embedded therein, wherein the ceramic body comprises a dissipation factor of about 0.11 to about 0.16 and a capacitance of about 750 picoFarads to about 950 picoFarads between the electrode and the one or more heating elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 61/638,871, filed Apr. 26, 2012, which application is herebyincorporated by reference herein.

BACKGROUND

1. Field

Embodiments of the invention generally relate to an electrostatic chuckhaving reduced power loss, and methods and apparatus for reducing powerloss in an electrostatic chuck, as well as methods for testing andmanufacture thereof.

2. Description of the Related Art

In the manufacture of electronic devices on substrates, such assemiconductors and displays, many vacuum processes are utilized, such aschemical vapor deposition (CVD), physical vapor deposition (PVD), etch,implant, oxidation, nitridation, or other processes, to form theelectronic devices. The substrates are typically processed one by one onan electrostatic chuck in a substrate processing chamber. To increasethroughput, modern manufacturers often utilize a plurality of thesesubstrate processing chambers operating in parallel (i.e., running acommon process recipe). Each of the processing chambers may be the samemake and model and are typically configured to process a substrateaccording to the common recipe. Thus, plural substrates may be processedwithin the same time period to produce identical product.

While the processing chambers may be substantially identical, subtlevariations may exist between the processing chambers. The variations mayrequire adjustment of the process parameters on one or more of theprocessing chambers to obtain “chamber match” or “chamber matching.” Onemethodology to reduce chamber on-wafer results in processing chambersutilizing radio frequency (RF) induced plasma processes modifies the RFpower parameters of a particular processing chamber to compensate for achamber-to-chamber variation in order produce a product that is intolerance with other products that are processed in other processingchambers according to the common recipe. However, to modify the RF powerparameters to obtain chamber matching, additional hardware is typicallyrequired. The additional hardware is often costly and typically does notaddress the root cause of the chamber-to-chamber variation.

Accordingly, it is desirable to reduce the chamber-to-chamber variationsin on-wafer results in order to streamline parallel processing ofsubstrates.

SUMMARY

Embodiments of the invention generally relate to an electrostatic chuckhaving reduced power loss, and methods and apparatus for reducing powerloss in an electrostatic chuck, as well as methods for testing andmanufacture thereof. In one embodiment, an electrostatic chuck isprovided. The electrostatic chuck includes a conductive base, and aceramic body disposed on the conductive base, the ceramic bodycomprising an electrode embedded therein, wherein the ceramic bodycomprises a dissipation factor of about 0.11 to about 0.16.

In another embodiment, a plasma reactor is provided. The plasma reactorincludes a vacuum chamber, an electrostatic chuck (ESC) within thechamber for supporting a substrate to be processed, and a radiofrequency (RF) supply voltage source coupled to an electrode disposedwithin the ESC. The ESC comprises a ceramic body coupled to a conductivebase, the ceramic body comprises a ceramic material having the electrodeembedded therein, and the ceramic material includes a dissipation factorof about 0.11 to about 0.16.

In another embodiment, a method for manufacturing a puck for anelectrostatic chuck is provided. The method includes placing a ceramicpowder in a mold, forming an electrode and one or more heating elementsin the ceramic powder, and sintering and/or pressing the ceramic powderto produce a ceramic body having a crystal structure with one or both ofa dissipation factor of about 0.11 to about 0.16 and a capacitance ofabout 750 picoFarads to about 950 picoFarads between the electrode andthe one or more heating elements.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic cross-sectional view of one embodiment of a plasmareactor.

FIG. 2A is a side cross-sectional view of an electrostatic chuckaccording to embodiments described herein.

FIG. 2B is an enlarged cross-sectional view of a portion of theelectrostatic chuck of FIG. 2A.

FIG. 3 is a schematic diagram of a puck showing RF power to the chuckingelectrode, the RF power to plasma and the RF power to heating elements.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments described herein generally relate to an electrostatic chuckfor use in a vacuum processing chamber. The electrostatic chuck hasreduced power loss, and methods and apparatus for reducing power loss inan electrostatic chuck, as well as methods for testing and manufacturethereof, are also provided. The methods and apparatus as describedherein reduce chamber to chamber variations and enable chamber matchingfor operating plural processing chambers in parallel.

FIG. 1 is a schematic cross-sectional view of one embodiment of a plasmareactor 100. The plasma reactor 100 comprises a vacuum chamber 110enclosing a processing volume 120. The processing volume 120 is definedby a cylindrical side wall 125 supporting a ceiling 130 that includes aprocess gas distribution showerhead 135. A process gas supply is coupledto the gas distribution showerhead 135. An electrostatic chuck (ESC) 140holds a substrate 145 in the vacuum chamber 110. The ESC 140 includes aconductive base 150 and a puck 155 that may be formed of a dielectricmaterial, such as a ceramic material. The puck 155 comprises a chuckingelectrode 160 and, in one embodiment, inner and outer heating elements165A, 165B. The chucking electrode 160 may comprise a conductive mesh ofa metal or metal alloy that is embedded within the puck 155. The innerand outer heating elements 165A, 165B may comprise a resistive heatingelement comprising a metal or metal alloy that is embedded within thepuck 155 beneath the chucking electrode 160. A vacuum pump is coupled tothe vacuum chamber 110 to generate a sub-atmospheric pressure within thevacuum chamber 110.

Two or more radio frequency (RF) bias power supplies are coupled to theprocess gas distribution showerhead 135 and one of the conductive base150 or the chucking electrode 160. A first RF power supply, such as anRF source generator 170A may be coupled to the process gas distributionshowerhead 135 and one of the conductive base 150 or the chuckingelectrode 160 through an impedance match circuit 175A to ignite a plasmaand provide a source of reactive species in the processing volume 120. Asecond RF power supply, such as a first bias RF generator 170B coupledto an impedance match circuit 175B may be used to control the criticalthin layer of plasma just above the substrate 145 within the processingvolume 120. An optional third RF power supply, such as a second bias RFgenerator 170C coupled to an impedance match circuit 175C may be used inconjunction with the one or both of the RF source generator 170A and thefirst bias RF generator 170B to modulate the plasma within theprocessing volume 120. The RF source generator 170A may provide RF powerof about 13.56 megaHertz (MHz) while the first bias RF generator 170Band/or the second bias RF generator 170C may provide bias RF power ofabout 2 MHz, 27 MHz and/or 60 MHz. The plasma reactor 100 also includesalternating current (AC) sources 180A, 180B to provide AC current to theinner and outer heating elements 165A, 165B through a low-pass filter185A and a low-pass filter 185B, respectively.

The chucking electrode 160 is a conductor, such as a metal or metalalloy. The chucking electrode 160 can be composed of various conductors,such as non-magnetic materials, for example aluminum, copper, iron,molybdenum, titanium, tungsten, or alloys thereof. One version of thechucking electrode 160 comprises a mesh of molybdenum. The chuckingelectrode 160 may be configured as a mono-polar or bi-polar electrode.Mono-polar electrodes comprise a single conductor and have a singleelectrical connection to an external electrical power source, such as adirect current (DC) chucking voltage supply. Mono-polar electrodescooperate with the charged species of a plasma formed in the processingvolume 120 to apply an electrical bias across the substrate 145 tosecure the substrate 145 on the ESC 140. Bi-polar electrodes have two ormore conductors, each of which is biased relative to the other togenerate an electrostatic force to secure the substrate 145 on the ESC140. The chucking electrode 160 can be shaped as a wire mesh or aperforated metal plate. For example, a chucking electrode 160 comprisinga mono-polar electrode can be a single continuous wire mesh embedded inthe puck 155 as shown. An embodiment of a chucking electrode 160comprising a bi-polar electrode can be two or more conductive membersthat may be independently biased by the DC chucking voltage supply.

In operation, direct current from the DC chucking voltage supply isapplied to the chucking electrode 160. The DC chucking voltage supply isutilized to monitor induced DC bias potential on the substrate 145,calculate the necessary voltage for reliable electrostatic clamping, andis used to apply the proper clamping voltage to the chucking electrode160. RF power from the RF source generator 170A is utilized to induce aplasma of process gas in the processing volume 120 above the substrate145. The plasma may be modified by one or both of the first bias RFgenerator 170B and the second bias RF generator 170C. The combination ofthe plasma overlying the substrate 145 and the voltage applied to thechucking electrode 160 induces an electrostatic charge between thesubstrate 145 and the puck 155, which attracts the substrate 145 to thepuck 155 surface. The substrate 145 may be processed on the ESC 140 attemperatures up to 600 degrees Celsius.

The RF power from the RF source generator 170A is used to produce plasmain the processing volume 120, which processes the substrate 145. Oncethe plasma is ignited, the amount of power from the RF source generator170A has generally a minor effect on process performance. On the otherhand, the first bias RF generator 170B provides a bias to the substrate145 on the puck 155 surface, which may additionally be used to controlthe parameters of the thin plasma layer just above the substrate 145surface. As stated above, the process parameters are weakly dependent onthe amount of source RF power, but strongly dependent on the bias RFpower delivered to the plasma from the ESC 140.

However, it has been determined that some of the RF power is lost toground. For example, some of the RF power is lost to ground by inductivecapacitance with the heating elements 165A, 165B. In another example,some of the RF power is lost to ground through the DC chucking voltagesupply. While the source power loss does not significantly affect theplasma, other parameters and subsystems of the plasma reactor 100 aregreatly affected by variations in bias RF power. For example, DC voltagemeasured or calculated by the DC chucking voltage supply may be unstabledue to changes in the thin plasma layer above the substrate 145 surface.For a single plasma reactor 100 operating separately from otherchambers, the power loss may be consistent substrate-to-substrate andmay go unnoticed. However, if the plasma reactor 100 is utilized inparallel with other similar chambers running the same recipe, the powerlosses of each chamber will likely vary, and adjustment and/orcorrective action may be required in order to match each chamber.

The inventors have devised test methods for testing of the ESC 140 todetermine physical properties of the ESC 140. The test methods asdescribed herein yielded critical dimensions and values that mitigatecapacitance to ground in the ESC 140. Thus, components of the ESC 140may be subjected to the test methods to determine critical physicalproperty values and dimensions prior to final assembly of the ESC 140.

FIG. 2A is a side cross-sectional view of an ESC 200 according toembodiments described herein. FIG. 2B is an enlarged cross-sectionalview of a portion of the ESC 200 of FIG. 2A. The ESC 200 may be utilizedas the ESC 140 in the plasma reactor 100 of FIG. 1. Common referencenumerals are utilized and the description of some elements may not berepeated for brevity.

The ESC 200 comprises the puck 155 which comprises a ceramic body 205.The chucking electrode 160 may be formed in the ceramic body 205 bymethods known in the art. In this embodiment, the ceramic body 205 iscoupled to a ceramic base 207. The ESC 200 also includes a plurality ofgas conduits 209 for providing a backside gas to a substrate (shown inFIG. 1). The heating elements 165A, 165B may be formed in the ceramicbase 207 as shown in FIG. 2A, or in the puck 155 as shown in FIG. 1. Theheating elements 165A, 165B may be formed in the ceramic base 207 bymethods known in the art. Such methods include spray coating a conductoronto the underside of the puck 155 or the upper surface ceramic base207, providing a pre-formed thin film electrode to the underside of thepuck 155 or the upper surface ceramic base 207, among other methods. Theceramic body 205 and the ceramic base 207 may be fabricated from aceramic material comprising at least one of aluminum oxide, aluminumnitride, silicon oxide, silicon carbide, silicon nitride, titaniumoxide, zirconium oxide, and mixtures thereof. The ceramic body 205 mayalso comprise a samarium aluminum oxide material, such as SmAl_(X)O_(Y).The ceramic body 205 can be unitary monolith of ceramic made by hotpressing and sintering a ceramic powder, and then machining the sinteredbody to form the final shape of the puck 155. An upper surface of theceramic body 205 defines a substrate receiving surface 210 that is thetop surface of the puck 155 and which serves to hold a substrate 145, asshown in FIG. 1. The ceramic base 207 can be unitary monolith of ceramicmade by hot pressing and sintering a ceramic powder, and then machiningthe sintered body to form the final shape of the ceramic base 207. Theceramic body 205 may be coupled to the ceramic base 207 by a binder oran adhesive as is known in the art.

According to embodiments described herein, the ceramic body 205 isprocessed (i.e., sintered, pressed) to produce a crystal structurehaving electrical characteristics that reduce RF losses to ground. Theceramic body 205 as described herein was tested at temperatures of aboutroom temperature to about 250 degrees Celsius (° C.) and the electricalcharacteristics were as follows. In one embodiment, the ceramic body 205comprises a dissipation factor (tangent δ) of about 0.10 to about 0.20at temperatures up to about 250° C., more specifically a dissipationfactor of about 0.11 to about 0.16 at temperatures of about roomtemperature to about 250° C. Additionally, the ceramic body 205comprises a capacitance to heating elements 165A, 165B of about 750picoFarads (pF) to about 950 pF between the chucking electrode 160 andthe heating elements 165A, 165B at temperatures of about roomtemperature to about 250° C. The puck 155, having one or more of thecapacitance and the dissipation factor described above, provides optimumRF power for plasma generation while minimizing RF losses to ground.

Referring to FIG. 2B, the ceramic body 205 of the puck 155 includes atop dielectric thickness, referred to as thickness D, indicating thethickness of dielectric material between the substrate receiving surface210 and an upper surface 215 of the chucking electrode 160. In oneembodiment, the thickness D is about 0.041 inches to about 0.044 inches.The puck 155 having the thickness D within these parameters providessufficient DC voltage to wafer capacitance while minimizing capacitanceto ground.

The puck 155 may be manufactured according to sintering temperaturesand/or pressure parameters that are known to those of skill in the art.The thickness D may be produced by a suitable mold and/or pressureprofiles during the sintering process. Machining the substrate receivingsurface 210 of the ceramic body 205 may be optionally performed toproduce the thickness D.

FIG. 3 is a schematic diagram of a puck 155 showing RF power to thechucking electrode 160, the RF power to plasma and the RF power toheating elements 165A, 165B. In this Figure, the ceramic body 205 issplit into a top portion 305A above the chucking electrode 160 and alower portion 305B below the chucking electrode 160. The following tablecompares various values between a conventional ESC and the ESC 140 asdescribed herein.

Ctop, Total RF loss, % nF Cbot, nF tan(δ) Conventional 37.5% 3.2 1.2 0.6ESC ESC 140 16.7% 3.2 0.8 0.2 Reduction >about 50% about 33% about 66%

Additionally, the ESC 140 included a top loss (RF loss to chuckingelectrode 160 from 305A) of 0.133333, as compared to the top loss in theconventional ESC of 0.272727 (e.g., about 50% reduction). The bottomloss (RF loss to heating elements 165A, 165B from 305B) of the ESC 140was 0.033333 as compared to 0.102273 in a conventional ESC (e.g., about66% reduction).

As is demonstrated, the ESC 140 as described herein provides superiorelectrical characteristics as compared to a conventional ESC. The puck155 of the ESC 140 may be manufactured according to sinteringtemperatures and/or pressure parameters that are known to those of skillin the art, and tested prior to shipment according to the followingprocedures.

Impedance testing of the puck 155 may be performed by clamping asubstrate to the ESC 140 with vacuum through the gas conduits 209 (shownin FIG. 2A). The RF terminal to the chucking electrode 160 is connectedto the positive (red) terminal of a capacitance meter and the negativeterminal (black) of the capacitance meter is coupled to the conductivebase 150 (shown in FIG. 1). The test will measure capacitance from theRF conductor to the substrate. The capacitance to heating elements 165A,165B and tangent δ may be tested with a LCZ meter while the puck 155 isin a temperature stabilized enclosure. Dielectric thickness (thickness D(FIG. 2B)) may be determined by various techniques, such as ultrasonicimaging or eddy current measurements.

The embodiments above provide a manufacturing protocol and designparameters for an electrostatic chuck that may be utilized in differentchambers running the same recipe with minimal to no variation in productand/or wafer-to-wafer results. The ESC 140 as described herein reducesRF losses to ground, which enhances process results. Additionally, ESC's140 produced according to the parameters described herein providesufficient DC voltage to wafer capacitance while minimizing capacitanceto ground, which enhances process results. Further, additional hardwareand/or adjustment of power supplies that may be necessary to mitigatechamber-to-chamber mismatches are not needed, which lowers the cost ofownership and streamlines processing, which increases throughput.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An electrostatic chuck, comprising: aconductive base; and a ceramic body disposed on the conductive base, theceramic body comprising an electrode embedded therein, wherein theceramic body comprises a dissipation factor of about 0.11 to about 0.16.2. The electrostatic chuck of claim 1, wherein the ceramic bodycomprises one or more heating elements embedded therein.
 3. Theelectrostatic chuck of claim 2, wherein the ceramic body comprises acapacitance of about 750 picoFarads to about 950 picoFarads between theelectrode and the one or more heating elements.
 4. The electrostaticchuck of claim 1, wherein the ceramic body comprises an outer heatingelement and an inner heating element.
 5. The electrostatic chuck ofclaim 4, wherein the ceramic body comprises a capacitance of about 750picoFarads to about 950 picoFarads between the electrode and the innerand outer heating elements.
 6. The electrostatic chuck of claim 1,wherein the ceramic body further comprises a top dielectric thickness ofabout 0.041 inches to about 0.044 inches between a surface of theelectrode and a surface of the ceramic body.
 7. The electrostatic chuckof claim 6, wherein the ceramic body comprises one or more heatingelements embedded therein.
 8. The electrostatic chuck of claim 7,wherein the ceramic body comprises a capacitance of about 750 picoFaradsto about 950 picoFarads between the electrode and the one or moreheating elements.
 9. A plasma reactor, comprising: a vacuum chamber; anelectrostatic chuck within the chamber for supporting a substrate to beprocessed, and a radio frequency supply voltage source coupled to anelectrode disposed within the electrostatic chuck, wherein theelectrostatic chuck comprises: a ceramic body coupled to a conductivebase, the ceramic body comprising a ceramic material having theelectrode embedded therein, wherein the ceramic material includes adissipation factor of about 0.11 to about 0.16.
 10. The plasma reactorof claim 9, wherein the electrostatic chuck further comprises one ormore heating elements embedded in the ceramic body.
 11. The plasmareactor of claim 10, wherein the ceramic material comprises acapacitance of about 750 picoFarads to about 950 picoFarads between theelectrode and the one or more heating elements.
 12. The plasma reactorof claim 9, wherein the ceramic body comprises an outer heating elementand an inner heating element.
 13. The plasma reactor of claim 12,wherein the ceramic body comprises a capacitance of about 750 picoFaradsto about 950 picoFarads between the electrode and the inner and outerheating elements.
 14. The plasma reactor of claim 9, wherein the ceramicbody further comprises a top dielectric thickness of about 0.041 inchesto about 0.044 inches between a surface of the electrode and a surfaceof the ceramic body.
 15. The plasma reactor of claim 14, wherein theceramic body comprises one or more heating elements embedded therein.16. The electrostatic chuck of claim 15, wherein the ceramic bodycomprises a capacitance of about 750 picoFarads to about 950 picoFaradsbetween the electrode and the one or more heating elements.